1. Field of the Invention
The present invention relates generally to recording data on photographic film and, more particularly, to writing data on a recordable photographic filmstrip and reading data from such a filmstrip.
2. Description of the Related Art
In typical cameras, a photographic filmstrip is withdrawn from a film cartridge, advanced past a rectangular exposure gate as frames of latent images are exposed, and wound up on a take-up spool until all potential frames of the filmstrip are exposed. Thereafter, the filmstrip is rewound into the film cartridge and the cartridge is removed for processing the frames of latent images to form positive transparencies or, in the case of photographic negative film, to form negatives for the printing of positive, enlarged prints therefrom.
In many cases, it is desirable to know data concerning the exposed frames. For example, the photographer may want to record exposure information such as shutter time, aperture opening, and the like. Such exposure information could be helpful in producing prints from the filmstrip. Exposure information can be used by a photographic printer in determining proper printer parameters, such as color balance and exposure time, to produce more pleasing prints and in making re-order prints the same as originals. Also, the photographer may want to record the date of taking the photograph.
Exposure information, date information, and other such data also can be used advantageously for other related photographic purposes. For example, automated printer systems are available that electronically scan the frames of a developed filmstrip to derive a set of digitized video image data. The video image data is processed to display a positive video image that approximates the color balance and brightness of the print that will be obtained. The exposure information can be helpful in processing the video image data and other data, such as the date and identification, can be incorporated into the finished prints. More recently, systems have been developed for scanning and digitizing the frames of developed filmstrips for transfer of the frames into other media, such as a compact disc (CD) format, for use in video CD display systems. These transfer processes can utilize the exposure information to good advantage.
One technique for recording photographic data for the uses described above is to write the data into a recording material provided on a recordable photographic filmstrip. A recordable photographic filmstrip generally comprises a photographic filmstrip with a magnetic recording material that is deposited on the filmstrip or is integrally formed with the film emulsion or substrate. The magnetic recording material typically is deposited in a thin transparent layer over the entire surface of the photographic filmstrip and is referred to as the magnetics-on-film (MOF) layer. As frames are exposed in the camera, one or more magnetic heads write the data into the MOF layer in longitudinal data tracks that typically extend along one edge of the filmstrip outside of the frames.
After all frames of the recordable filmstrip are exposed with latent images and the associated data is written into the MOF layer, the filmstrip is processed to develop the latent images. The processing does not alter the recorded data, which can be retrieved by printers, scanning equipment, and other systems provided with suitable magnetic read heads. The recording of data into an MOF layer of a photographic filmstrip is described, for example, in U.S. Pat. No. 4,975,732 to Robison et al.
Such data recording techniques are convenient because the data is written into the MOF layer adjacent to the photographic frame with which it is associated and therefore is not likely to become separated or lost. Therefore, the data is readily available and can be quickly retrieved. Moreover, the photographer need not take any special action to record the data, as the recording of data into the MOF layer ordinarily is automatically carried out by the camera. Finally, additional information can be written into the MOF layer after the original exposure and processing. For example, the digitized video image data associated with a frame can be written into the MOF layer adjacent the frame.
In cameras that record data into the MOF layer of a recordable photographic filmstrip, a magnetic write head typically is provided in the film path of the camera adjacent the film gate for writing the data into the MOF layer. Accordingly, a system that is to retrieve the data after the filmstrip has been developed, such as a printer or digitizing processor, must include a magnetic read head. Thus, cameras must write the data into tracks in the MOF layer at predetermined locations of the filmstrip to record the data and processors must precisely locate and follow the data tracks in the MOF layer to read the data. Therefore, the magnetic heads must be positioned accurately to ensure correct writing and reading of the data.
Conventionally, the data is written by a data recording camera having a magnetic write head that is located a predetermined distance from the film edge and is read by a processor having a reading assembly that includes a magnetic read head and a guide plate that is located a predetermined distance from the magnetic read head. In the processor, during the printing or digitizing of the developed frames, the guide plate physically presses against the edge of the filmstrip to position the magnetic read head at the predetermined distance from the edge, where the data tracks were written. The filmstrip is kept under tension in the printer and therefore is held substantially taut against the pressure of the guide plate.
Unfortunately, pressing the guide plate of the reading assembly against the filmstrip edge can damage the filmstrip. Moreover, the filmstrip is relatively thin and therefore somewhat flexible, such that the position of the magnetic head can move slightly as the guide plate is pressed against the filmstrip, even though the filmstrip is held substantially taut. Hence, pressing the guide plate against the filmstrip does not consistently position the read head with great accuracy. These problems make it difficult to obtain consistent and accurate data recording. Such problems tend to be exacerbated as the filmstrip ages. In addition, adapting the printer to write supplemental data into the MOF layer is made less practical with potentially inaccurate positioning of the read/write head assembly. Finally, mechanical guide plates can effectively limit the processing speed of printers because the film damage and inaccurate positioning generally must be decreased by reducing the speed of the filmstrip through the printer.
From the discussion above, it should be apparent that there is a need for a data recording system that can accurately and consistently write data into tracks at a predetermined location in a recordable photographic filmstrip and then read such data from those tracks without damaging the filmstrip. The present invention satisfies this need.